Actuation of shape memory alloy materials using ultracapacitors

ABSTRACT

A system, in certain embodiments, includes a power supply. The power supply includes an ultracapacitor configured to be charged by a DC source. The power supply also includes a first switch that enables charging of the ultracapacitor by the DC source when in a closed position and disables charging of the ultracapacitor when in an open position. The power supply further includes a second switch configured to enable discharging of the ultracapacitor when in a closed position and to disable discharging of the ultracapacitor when in an open position. As the ultracapacitor is discharged, a current is supplied to actuate a shape memory alloy element.

BACKGROUND

This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

Deepwater accumulators provide a supply of pressurized working fluid for the control and operation of sub-sea equipment, such as through hydraulic actuators and motors. Typical sub-sea equipment may include, but is not limited to, blowout preventers (BOPS) that shut off the well bore to protect an oil or gas well from accidental discharges to the environment, gate valves for flow control of oil or gas to the surface or to other sub-sea locations, electro-hydraulic control pods, or hydraulically-actuated connectors and similar devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying figures in which like characters represent like parts throughout the figures, wherein:

FIG. 1 is a schematic of an embodiment of a sub-sea BOP stack assembly having one or more shape memory alloy (SMA)-powered hydraulic accumulators;

FIG. 2 is a schematic of an embodiment of a SMA wire being used to lift a weight;

FIG. 3 is a graph of a SMA transitioning from an Austenite phase to a Martensite phase and back;

FIG. 4 is a perspective view of an embodiment of an SMA-powered hydraulic accumulator;

FIG. 5 is a schematic of an embodiment of the SMA-powered hydraulic accumulator of FIG. 4 with an associated power supply, controller, and sensor;

FIG. 6 is a schematic of an embodiment of an SMA-powered drive configured to drive a mineral extraction component;

FIG. 7 is a perspective view of an embodiment of an SMA-powered hydraulic accumulator having perforated actuation plates, wire guides, and wire clamps;

FIG. 8 is a cutaway perspective view of the SMA-powered hydraulic accumulator of FIG. 7, illustrating a portion of the SMA wires removed to show internal details;

FIG. 9 is a cross-sectional view of the SMA-powered hydraulic accumulator of FIG. 7;

FIG. 10 is a partial perspective view of the SMA-powered hydraulic accumulator of FIG. 7 taken within line 10-10, illustrating details of the wire guides;

FIG. 11 is a perspective view of an embodiment of a perforated top plate of the SMA-powered hydraulic accumulator of FIG. 7, illustrating a wire guide exploded from a pair of wire openings in the perforated top plate;

FIG. 12 is a perspective view of an embodiment of a wire guide;

FIG. 13 is a partial perspective view of an embodiment of the SMA-powered hydraulic accumulator of FIG. 7 taken within line 13-13, illustrating details of the wire clamps;

FIG. 14 is a perspective view of an embodiment of a perforated bottom plate of the SMA-powered hydraulic accumulator of FIG. 7, illustrating a wire guide and a wire clamp exploded from wire openings in the perforated bottom plate;

FIG. 15 is a perspective view of an embodiment of a wire clamp, illustrating a pair of wire clamp plates and an insulating wire sleeve;

FIG. 16 is a perspective view of an embodiment of one of the wire clamp plates of FIG. 15;

FIG. 17 is a top view of an embodiment of the wire clamp of FIG. 15;

FIG. 18 is a simplified block diagram illustrating an embodiment of an SMA-powered application having SMA elements that may be actuated by power supplies configured to provide an actuation charge to the SMA elements via one or more ultracapacitors;

FIGS. 19-21 are circuit schematic diagrams that depict the operation of an ultracapacitor-based power supply, in accordance with an embodiment;

FIG. 22 is a more detailed circuit schematic diagram showing another embodiment of the ultracapacitor-based power supply;

FIG. 23 is a more detailed circuit schematic diagram showing a further embodiment of the ultracapacitor-based power supply;

FIG. 24 is a flow chart depicting an embodiment of a method for actuating an SMA element using an ultracapacitor-based power supply; and

FIG. 25 is a graph depicting examples of ultracapacitor discharge profiles.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present invention will be described below. These described embodiments are only exemplary of the present invention. Additionally, in an effort to provide a concise description of these exemplary embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Moreover, the use of “top,” “bottom,” “above,” “below,” and variations of these terms is made for convenience, but does not require any particular orientation of the components.

Accumulators may be divided into a gas section and a hydraulic fluid section that operate on a common principle. The general principle is to pre-charge the gas section with pressurized gas to a pressure at or slightly below the anticipated minimum pressure to operate the sub-sea equipment. Fluid can be added to the accumulator in the separate hydraulic fluid section, compressing the gas section, thus increasing the pressure of the pressurized gas and the hydraulic fluid together. The hydraulic fluid introduced into the accumulator is therefore stored at a pressure equivalent to the pre-charge pressure and is available for doing hydraulic work. However, gas-charged accumulators used in sub-sea environments may undergo a decrease in efficiency as water depth increases. This loss of efficiency is due, at least in part, to an increase of hydrostatic stress acting on the pre-charged gas section, which provides the power to the accumulators through the compressibility of the gas.

The pre-charge gas can be said to act as a spring that is compressed when the gas section is at its lowest volume and greatest pressure and released when the gas section is at its greatest volume and lowest pressure. Accumulators may be pre-charged in the absence of hydrostatic pressure and the pre-charge pressure may be limited by the pressure containment and structural design limits of the accumulator vessel under surface ambient conditions. Yet, as described above, as accumulators are used in deeper water, their efficiency decreases as application of hydrostatic pressure causes the gas to compress, leaving a progressively smaller volume of gas to charge the hydraulic fluid. The gas section must consequently be designed such that the gas still provides enough power to operate the sub-sea equipment under hydrostatic pressure even as the hydraulic fluid approaches discharge and the gas section is at its greatest volume and lowest pressure.

For example, accumulators at the surface may provide 3,000 psi (pounds per square inch) maximum working fluid pressure. In 1,000 feet of seawater, the ambient pressure is approximately 465 psi. Therefore, for an accumulator to provide a 3,000 psi differential at the 1,000 foot depth, it must actually be pre-charged to 3,000 psi plus 465 psi, or 3,465 psi. At slightly over 4,000 feet water depth, the ambient pressure is almost 2,000 psi. Therefore, the pre-charge would be required to be 3,000 psi plus 2,000 psi, or 5,000 psi. In others words, the pre-charge would be almost double the working pressure of the accumulator. Any fluid introduced for storage may cause the pressure to exceed the working pressure and may lead to accumulator failure. Thus, at progressively greater hydrostatic operating pressures, the accumulator has greater pressure containment requirements at non-operational (e.g., no ambient hydrostatic pressure) conditions.

Given the limited structural capacity of the accumulator to safely contain the gas pre-charge, operators of this type of equipment may be forced to work within efficiency limits of the systems. For example, when deep water systems are required to utilize hydraulic accumulators, operators will often add additional accumulators to the system. Some accumulators may be charged to 500 psi, 2,000 psi, 5,000 psi, or higher, based on system requirements. As the equipment is initially deployed in the water, all accumulators may operate normally. However, as the equipment is deployed in deeper water (e.g., past 1,000 feet), the accumulators with the 500 psi pre-charge may become inefficient due to the hydrostatic compression of the gas charge. Additionally, the hydrostatic pressure may act on all the other accumulators, decreasing their efficiency. The decrease in efficiency of the sub-sea gas charged accumulators decreases the amount and rate of work which may be performed at deeper water depths. As such, for sub-sea equipment designed to work beyond 5,000 foot water depth, the amount of gas charged accumulators must be increased by 5 to 10 times. The addition of these accumulators increases the size, weight, and complexity of the sub-sea equipment, in addition to generating hundreds of potential additional failure points, all of which increases the cost and potential risk of equipment failure.

Conversely, the disclosed embodiments do not rely on gas to provide power for the accumulator. Rather, shape memory alloy (SMA) wires acting in tension on a piston provide the power. In addition, the back side of the piston may be balanced with the hydrostatic pressure at any water depth. This may be achieved through the use of a “sea chest,” which is a rubber bladder which transfers hydrostatic pressure (from the water depth) to a fluid (e.g., the dielectric fluid on the back side of the SMA accumulator piston) on the other side. This means that the SMA material need only generate a reduced amount of power (compared to non-balanced accumulators) since it does not need to overcome the hydrostatic pressure load and no loss of efficiency is experienced due to water depth. Additionally, the SMA-powered hydraulic accumulator is not limited to constant pressure output since the actuation current of the SMA materials may be adjusted. Furthermore, the power output of the SMA materials may be adjusted without the need for pumps or valves. This may allow for the adjustment of output pressure from the accumulator, further increasing the flexibility of the equipment. In addition, leak paths may be substantially reduced using the disclosed embodiments. As discussed further below, the SMA-powered hydraulic accumulator may be used in various types of equipment.

Further, in accordance with certain disclosed embodiments, an SMA-powered hydraulic accumulator, as well as other SMA-powered systems, may be driven or actuated using a power system that includes one or more electric double-layer capacitors, also referred to as supercapacitors or ultracapacitors. As will be appreciated, “ultracapacitors” are electrochemical capacitor devices that provide high energy density (e.g., typically hundreds to thousands of times greater) compared to conventional dielectric capacitors. As discussed in detail below, certain benefits that ultracapacitors exhibit over conventional capacitors and batteries make them particularly ideal for powering certain subsea applications, such as the above-mentioned SMA-powered hydraulic accumulators.

With the foregoing in mind, FIG. 1 depicts a sub-sea BOP stack assembly 10, which may include one or more large SMA-powered hydraulic accumulators 12 and/or one or more small SMA-powered hydraulic accumulators 13. The small SMA-powered hydraulic accumulators 13 may function similarly to the large SMA-powered hydraulic accumulators described herein, except that the small SMA-powered hydraulic accumulators 13 may be used for smaller sizes and capacities than the large SMA-powered hydraulic accumulators 12. As illustrated, the BOP stack assembly 10 may be assembled onto a wellhead assembly 14 on the sea floor 15. The BOP stack assembly 10 may be connected in line between the wellhead assembly 14 and a floating rig 16 through a sub-sea riser 18. The BOP stack assembly 10 may provide emergency fluid pressure containment in the event that a sudden pressure surge escapes the well bore 20. Therefore, the BOP stack assembly 10 may be configured to prevent damage to the floating rig 16 and the sub-sea riser 18 from fluid pressure exceeding design capacities. The BOP stack assembly 10 may also include a BOP lower riser package 22, which may connect the sub-sea riser 18 to a BOP package 24.

In certain embodiments, the BOP package 24 may include a frame 26, BOPS 28, and SMA-powered hydraulic accumulators 12, which may be used to provide backup hydraulic fluid pressure for actuating the BOPS 28. The SMA-powered hydraulic accumulators 12 may be incorporated into the BOP package 24 to maximize the available space and leave maintenance routes clear for working on components of the sub-sea BOP package 24. The SMA-powered hydraulic accumulators 12 may be installed in parallel where the failure of any single SMA-powered hydraulic accumulator 12 may prevent the additional SMA-powered hydraulic accumulators 12 from functioning.

In general, SMAS are materials which have the ability to return to a predetermined shape when heated. More specifically, when SMAS are below their transformation temperature, they have relatively low yield strengths and may be deformed into and retain any new shape relatively easy. However, when SMAS are heated above their transformation temperature, they undergo a change in crystal structure, which causes them to return to their original shape with much greater force than from their low-temperature state. During phase transformations, SMAS may either generate a relatively large force against any encountered resistance or undergo a significant dimension change when unrestricted. This shape memory characteristic may provide a unique mechanism for remote actuation.

One particular shape memory material is an alloy of nickel and titanium called Nitinol. This particular alloy is characterized by, among other things, long fatigue life and high corrosion resistance. Therefore, it may be particular useful as an actuation mechanism within the harsh operating conditions encountered with sub-sea mineral extraction applications. As an actuator, it is capable of up to approximately 5% strain recovery or approximately 500 MPa restoration stress with many cycles, depending upon the material composition. For example, a Nitinol wire 0.5 mm in diameter may generate as much as approximately 15 pounds of force. Nitinol also has resistance properties which enable it to be actuated electrically by heating. In other words, when an electric current is passed directly through a Nitinol wire, it can generate enough heat to cause the phase transformation. In addition, other methods of heating the SMA wire may be utilized. Although Nitinol is one example of an SMA which may be used in the SMA-powered hydraulic accumulators 12 and 13 of the disclosed embodiments, any SMAS with suitable transition temperatures and other properties may also be used. In many cases, the transition temperature of the SMA may be chosen such that surrounding temperatures in the operating environment are well below the Martensite transformation point of the material. As such, the SMA may be actuated only with the intentional addition of heat.

The unique properties of SMAS make them a potentially viable choice for actuators. For example, when compared to piezoelectric actuators, SMA actuators may offer an advantage of being able to generate larger deformations and forces at much lower operating frequencies. In addition, SMAS may be fabricated into different shapes, such as wires and thin films. In particular, SMA wires with diameters less then 0.75 mm may be used to form stranded cables for use in the SMA-powered hydraulic accumulators 12. Accordingly, SMA-powered actuators such as the SMA-powered hydraulic accumulators 12 described herein may be used in myriad applications. For example, the SMA wires described below may be used in SMA-powered actuators such as hydraulic actuators, pneumatic actuators, mechanical actuators, and so forth. However, as described herein, the use of SMA wires may provide particular benefits in the realm of sub-sea equipment, such as the SMA-powered hydraulic accumulators 12 described in FIG. 1.

FIG. 2 depicts an exemplary SMA wire 30 being used to lift a weight 32. In particular, moving from left to right, FIG. 2 illustrates a time series whereby an electrical current may be introduced through the SMA wire 30 to gradually heat the SMA wire 30 and then gradually cool the SMA wire 30. In particular, at initial time t₀, no electrical current flows through the SMA wire 30. At time t₀, the SMA wire 30 may be at a temperature below the transition temperature of the SMA wire 30. As such, the SMA wire 30 may have been extended to a deformed shape by the force applied to the SMA wire 30 by the weight 32. Once electrical current is applied to the SMA wire 30, the temperature of the SMA wire 30 may gradually increase such that the transition temperature of the SMA wire 30 may be exceeded. When this occurs, the SMA wire 30 may begin returning to its predetermined shape such that the gravitational force applied by the weight 32 may be overcome, resulting in the SMA wire 30 lifting the weight 32, as shown at time t₁. At some point, such as time t₂, the force applied by the weight 32 may be entirely overcome such that the SMA wire 30 returns to its predetermined shape. Therefore, from time t₀ to time t₂, the SMA wire 30 may be heated and, as a result, may contract and overcome the force of the weight 32. As described above, as the temperature of the SMA wire 30 increases through the transition temperature, the SMA wire 30 may either generate a relatively large force against any encountered resistance (e.g., against the force of the weight 32), undergo a significant dimension change when unrestricted (e.g. lifting the weight 32), or generate some force and undergo some dimension change at the same time (e.g., lifting the weight 32 to some distance below its predetermined state).

Conversely, at time t₃, the electrical current may cease flowing through the SMA wire 30. Once the electrical current ceases flowing through the SMA wire 30, the temperature of the SMA wire 30 may gradually decrease to below the transition temperature of the SMA wire 30. When this occurs, the force of the weight 32 may begin deforming the SMA wire 30, as shown at time t₄. At some point, such as time t₅, the force applied by the weight 32 may entirely overcome the SMA wire 30, extending it to the deformed shape from time t₀. Therefore, from time t₃ to time t₅, the SMA wire 30 may be cooled and, as a result, may extend due to the force of the weight 32. As the temperature of the SMA wire 30 decreases through the transition temperature, the SMA wire 30 may undergo a significant dimension change when unrestricted (e.g. in allowing the weight 32 to lower).

The unique properties of SMAS result from the reversible phase transformation between their crystal structures, for instance, the stronger high temperature Austenite phase and the weaker low temperature Martensite phase. FIG. 3 depicts an SMA transitioning from the Austenite phase to the Martensite phase and back. When cooling from its high temperature Austenite phase 34, the SMA undergoes a transformation to a twinned Martensite phase 36. The twinned Martensite phase 36 may be easily deformed by an external force. This process is often called de-twinning. The Martensite phase 38 is then reversed when the de-twinned structure reverts upon heating to the Austenite phase 34. The unique ability of a reversible crystalline phase transformation enables an SMA object either to recover its initial heat-treated shape (up to approximately 5% strain) when heated above a critical transition temperature or alternatively to generate high recovery stresses (in excess of 500 MPa). As shown in FIG. 3, the transformation exhibits a hysteretic effect, in that the transformations on heating and on cooling do not overlap. This hysteretic effect may be taken into account by a feedback control system with appropriate hysteresis compensation to achieve higher precision in either a position control or a force control system.

FIG. 4 depicts an exemplary embodiment of an SMA-powered hydraulic accumulator 12. As illustrated, the SMA-powered hydraulic accumulator 12 may include a frame 40 through which a rod 42 may extend. At least one frame support 44 may support the rod 42 within the frame 40. In particular, the rod 42 may pass through apertures 46 in each of the frame supports 44. More specifically, linear bearings 48 may support the rod 42 within the frame supports 44. As such, the linear bearings 48 may enable axial movement along a longitudinal axis 50 of the SMA-powered hydraulic accumulator 12.

In the present context, the term “proximal” generally refers to ends of components of the SMA-powered hydraulic accumulator 12 which are closer to a fluid inlet/outlet 52 of the SMA-powered hydraulic accumulator 12. Conversely, the term “distal” generally refers to ends of components of the SMA-powered hydraulic accumulator 12 which are farther away from the fluid inlet/outlet 52 of the SMA-powered hydraulic accumulator 12.

The rod 42 may be connected at a distal end to a first end cap 54 and at a proximal end to a piston 56. The piston 56 may fit inside and mate with an inner cylinder 58, forming a hydraulic seal within which fluid 60 may be accumulated. In addition, the piston 56 may be configured to move axially within the inner cylinder 58 when the rod 42 moves axially in the same direction, thereby adjusting the interior volume of the inner cylinder 58 within which the fluid 60 accumulates. The inner cylinder 58 may be connected at a distal end to a proximal frame support 44 and at a proximal end to a second end cap 62. The fluid 60 may enter and exit a proximal section of the inner cylinder 58 via the fluid inlet/outlet 52. In addition, in certain embodiments, the inner cylinder 58 may be radially surrounded by an outer cylinder 64 which may isolate the inner cylinder 58 from harsh external environmental conditions.

In certain embodiments, SMA wires 30 may be wrapped around the first and second end caps 54, 62 as illustrated in FIG. 4. For instance, the SMA wires 30 may form a plurality of continuous lengths of stranded or braided cables which extend from the first end cap 54 to the second end cap 62, wrap around the second end cap 62, extend from the second end cap 62 to the first end cap 54, and wrap around the first end cap 54. As such, the SMA wires 30 may generally be located on opposite sides of the SMA-powered hydraulic accumulator 12. However, in other embodiments, the SMA wires 30 may be located on all sides of the SMA-powered hydraulic accumulator 12. Indeed, in certain embodiments, instead of using SMA wires 30 as illustrated in FIG. 4, the SMA-powered hydraulic accumulator 12 may utilize thin films of SMA material, which may stretch from the first end cap 54 to the second end cap 62. Moreover, other arrangements of SMA material may be utilized.

In certain embodiments, the manner in which the SMA wires 30 are wrapped around the first and second end caps 54, 62 may be facilitated by the shape of the first and second end caps 54, 62, as shown in FIG. 4. More specifically, the cross-section of the first and second end caps 54, 62 may be semi-circular in nature, as shown. In addition, in certain embodiments, grooves may be extruded in the externally-facing surfaces 66, 68 of the first and second end caps 54, 62, respectively, within which the SMA wires 30 may be secured. In addition, in certain embodiments, the SMA wires 30 and/or grooves may be coated with a suitable electrically non-conductive material for electrical isolation of the SMA wires 30 from the rest of the system (e.g., for safety of the operators and other systems). Furthermore, in certain embodiments, other suitable fasteners may be used to secure the SMA wires 30 to the externally-facing surfaces 66, 68 of the first and second end caps 54, 62, respectively.

The SMA-powered hydraulic accumulator 12 may be designed such that normal operating temperatures are substantially below the transition temperature of the SMA wires 30. As such, the SMA wires 30 may normally be allowed to deform when subjected to particular forces. In particular, the fluid 60 within the inner cylinder 58 may be pressurized (e.g., by hydraulic and hydrostatic pressures). The pressure in the fluid 60 may exert axial forces F_(axial) on a proximal face 70 of the piston 56 along the longitudinal axis 50. These axial forces F_(axial) may urge the piston 56 to move distally along the longitudinal axis 50, as illustrated by arrow 72, allowing more fluid 60 to enter the inner cylinder 58. This axial movement of the piston 56 may force the rod 42 and the first end cap 54 to move distally along the longitudinal axis 50 as well. However, the second end cap 62 may generally remain in a fixed position. Therefore, under normal operating temperatures, the SMA wires 30 which are wrapped around the first and second end caps 54, 62 of the SMA-powered hydraulic accumulator 12 may be stretched as a result of the hydraulic and/or hydrostatic pressures of the fluid 60 within the inner cylinder 58. In particular, this stretching of the SMA wires 30 may generally occur axially along the longitudinal axis 50, as again illustrated by arrow 72.

However, once an electrical current begins flowing through the SMA wires 30, the temperature within the SMA wires 30 may begin to increase. At some point, the temperature may exceed the transition temperature for the SMA material used in the SMA wires 30. Once the transition temperature of the SMA wires 30 is exceeded, the SMA wires 30 may begin to contract toward their predetermined shape. The contraction of the SMA wires 30 may force the first and second end caps 54, 62 to move together axially along the longitudinal axis 50. More specifically, the second end cap 62 may again generally remain in its fixed position while the first end cap 54 may move axially toward the second end cap 62 (i.e., toward the proximal end of the SMA-powered hydraulic accumulator 12), as illustrated by arrow 74. As the second end cap 54 moves axially closer to the proximal end of the SMA-powered hydraulic accumulator 12, the rod 42 may also move in the same direction axially and may begin to force the piston 56 in the same axial direction as well. As such, the piston 56 may begin to counteract the axial forces F_(axial) exerted by the pressure of the fluid 60 within the inner cylinder 58. As such, the piston 56 may begin displacing the fluid 60 within the inner cylinder 58, causing the fluid 60 to exit through the fluid inlet/outlet 52.

At some point, the SMA wires 30 may be restored to their predetermined shape and further heating via electrical current may no longer cause the SMA wires 30 to further contract. In certain embodiments, the SMA-powered hydraulic accumulator 12 may be designed such that the predetermined shape of the SMA wires 30 corresponds to a location of the piston 56 within the inner cylinder 58 which may cause substantially all of the volume of the fluid 60 to be evacuated from the inner cylinder 58. Likewise, in certain embodiments, the SMA-powered hydraulic accumulator 12 may be designed such that the maximum deformation shape for the SMA wires 30 corresponds to a location of the piston 56 within the inner cylinder 58 which may cause substantially all of the volume of the inner cylinder 58 to be filled with the liquid 60. However, in other embodiments, the predetermined shape and maximum deformation shape of the SMA wires 30 may correspond to other locations of the piston 56 within the inner cylinder 58.

In addition, in certain embodiments, the SMA-powered hydraulic accumulator 12 may be designed slightly differently. For example, in certain embodiments, the SMA-powered hydraulic accumulator 12 may not include a rod 42 connected between the first end cap 54 and the piston 56. Rather, in this embodiment, the first end cap 54 may instead be connected directly to the piston 56, which may extend distally from the inner cylinder 58 by a certain amount to allow for expansion and contraction of the SMA wires 30. Indeed, in certain embodiments, the SMA-powered hydraulic accumulator 12 may not include a first end cap 54. Rather, the SMA wires 30 may be wrapped directly around the piston 56.

The amount of volume of fluid 60 that the SMA-powered hydraulic accumulator 12 may be capable of displacing may vary based on the particular size of the SMA-powered hydraulic accumulator 12, the type of fluid 60 used, the pressure of the fluid 60, the type of SMA material used for the SMA wires 30, and so forth. In addition, although described herein as including a plurality of SMA wires, the SMA-powered hydraulic accumulator 12 may actually incorporate other designs for the SMA materials which provide the actuation power. For instance, in certain embodiments, the SMA materials may be in the shape of continuous, thin films which may wrap around the first and second end caps 54, 62 of the SMA-powered hydraulic accumulator 12.

As described above, the SMA-powered hydraulic accumulator 12 may be used in several different sub-sea applications, such as BOPS, gate valves, or hydraulic actuator and similar devices. For example, as illustrated in FIG. 1, the BOP stack assembly 10 may include a plurality of SMA-powered hydraulic accumulators 12 working in parallel. The SMA-powered hydraulic accumulators 12 described herein may generally operate at lower frequencies than conventional hydraulic accumulators. However, since the SMA-powered hydraulic accumulators 12 act in tension on the piston 56 to provide power, do not need to overcome the hydrostatic pressure load, and do not experience efficiency loss due to water depth, the SMA-powered hydraulic accumulators 12 are generally more efficient than conventional hydraulic accumulators.

FIG. 5 is an exemplary embodiment of the SMA-powered hydraulic accumulator 12 of FIG. 4 with an associated power supply 76, controller 78, and sensor 80, which may be a single or group of pressure and/or displacement and/or force sensors. As illustrated, in certain embodiments, the SMA wires 30 of the SMA-powered hydraulic accumulator 12 may be heated with current from the power supply 76 via actuation wires 82. The power supply 76 may either be an alternating current (AC) or direct current (DC) power supply. In general, the use of AC power may be the easier and least expensive option (e.g., using a transformer). However, the use of DC power may be the more self-sustainable option (e.g., a battery and capacitor) given the remote nature of most sub-sea applications. As will be discussed in detail below with respect to FIGS. 18-25, the power supply 76, in one embodiment, may include an ultracapacitor. For instance, the ultracapacitor may be charged by a DC source under the control of a DC charging controller. Once charged, the energy stored in the ultracapacitor may be discharged at a controlled rate by a discharge controller, which may be separate from or integrated with the DC charging controller. The discharged energy may be used to drive the SMA wires 30 into a contracted or actuated state (e.g., transition to the Austenite state).

In certain embodiments, the supply of current to the SMA wires 30 via the actuation wires 82 may be controlled by the controller 78. In certain embodiments, the controller 78 may include a memory device and a machine-readable medium with instructions encoded thereon for determining how much (if any) current should be supplied from the power supply 76 to the SMA wires 30 of the SMA-powered hydraulic accumulator 12. In certain embodiments, the controller 78 may be configured to receive feedback from the sensor 80 attached to the SMA-powered hydraulic accumulator 12 and/or the application (e.g., the BOP stack assembly 10 of FIG. 1) within which the SMA-powered hydraulic accumulator 12 is being used to determine whether, and how much, current should be supplied to the SMA wires 30 via the actuation wires 82. For example, in certain embodiments, the controller 78 may be configured to receive sensor measurements (e.g., pressure measurements, temperature measurements, flow rate measurements, displacement measurements, and so forth) from the SMA-powered hydraulic accumulator 12 and/or the application within which the SMA-powered hydraulic accumulator 12 is being used. The controller 78 may use the sensor measurements to vary the amount of current supplied to the SMA wires 30. In certain embodiments, the controller 78 may contain specific code for determining a relationship between the current supplied to the SMA wires 30, the temperature of the SMA wires 30, the amount of deformation of the SMA wires 30 corresponding to changes in temperature, and so forth. For example, as described above, the amount of deformation of the SMA wires 30 may depend on the transition temperature of the SMA material used for the SMA wires 30. Further, in an embodiment where the SMA material is driven using an ultracapacitor-based power supply, the sensor 80 may be configured to sense when the ultracapacitor is fully charged, and may signal the controller 78 to initiate a controlled discharge of energy stored within the ultracapacitor to supply current to the SMA wires 30 for actuation.

Since the controller 78 may be capable of adjusting the current supplied to the SMA wires 30, the SMA-powered hydraulic accumulator 12 is not limited to constant pressure output. Furthermore, the power output of the SMA-powered hydraulic accumulator 12 may be adjusted without the need for pumps or valves, further increasing the flexibility of the SMA-powered hydraulic accumulator 12, among other things.

Moreover, the disclosed embodiments may be extended to include other type of SMA-powered drives configured to drive various mineral extraction components. For example, FIG. 6 is an exemplary embodiment of an SMA-powered drive 84 which may be used to drive a mineral extraction component 86. A power supply 88, similar to the power supply 76 illustrated in FIG. 5, may be coupled to the SMA-powered drive 84 and a controller 90, similar to the controller 78 illustrated in FIG. 5, may be configured to adjust the power of the SMA-powered drive 84 to control a force generated by the SMA-powered drive 84 and sensor 92, similar to sensor 80 in FIG. 5, may be coupled to the mineral extraction component 86 or in between the mineral extraction component 86 and the SMA-powered drive 84. As described above, the force generated by the SMA-powered drive 84 may be cyclical based on the application of current from the power supply 88 to the SMA-powered drive 84. In general, the SMA-powered drive 84 may operate at somewhat lower frequencies but, depending on the particular design, may be capable of generating high forces. For example, in certain embodiments, the mineral extraction component 86 may be a fluid pump configured to be driven by the SMA-powered drive 84. Other types of mineral extraction components 86 which may be driven by the SMA-powered drive 84 may include, but are not limited to, pumps, compressors, valves, accumulators, and so forth. In addition, other types of equipment, other than mineral extraction equipment, may also be driven by the SMA-powered drive 84 using the disclosed techniques.

FIG. 7 is a perspective view of another embodiment of an SMA-powered hydraulic accumulator 100 having perforated actuation plates, wire guides, and wire clamps. As illustrated the SMA-powered hydraulic accumulator 100 includes a plurality of SMA wires 102 extending between a perforated top actuation plate 104 and a perforated bottom actuation plate 106. The top and bottom plates 104 and 106 are perforated with a plurality of wire openings 105 and 107, which pass the SMA wires 102 back and forth through the respective plates 104 and 106. The wire openings 105 and 107 are configured to maintain a desired spacing and alignment of the SMA wires 102 between the plates 104 and 106. In certain embodiment, a single SMA wire 102 may wind back and forth between the top and bottom plates 104 and 106. However, in the illustrated embodiment, one SMA wire 102 winds back and forth between the top and bottom plates 104 and 106 for each circular arrangement of wire openings 105 and 107. Thus, the illustrated embodiment includes a number of SMA wires 102 for the five concentric circular arrangements of SMA wires 102 winding back and forth between the top and bottom plates 104 and 106 (i.e., one SMA wire 102 per circular arrangement). Other embodiments may include more or fewer circular arrangements of SMA wires 102. Additionally, in further embodiments, the SMA wires 102 may be configured in arrangements of other types of enclosed shapes or polygons, such as squares, rectangles, triangles, etc., as well as other types of arrangements, such as Z-shaped or M-shaped arrangements, that do not necessarily form an enclosed shape.

At the top plate 104 and the bottom plate 106, the accumulator 100 includes a plurality of insulating wire guides 108 to gradually turn the SMA wires 102 in and out of the wire openings 105 and 107. As discussed below, the insulating wire guides 108 may have a curved path, such as a U-shaped path, that gradually bends the SMA wire 102 over a curvature of approximately 180 degrees. In this manner, the insulating wire guides 108 enable the SMA wire 102 to extend back and forth multiple times between the top and bottom plates 104 and 106, rather than requiring a pair of wire clamps at opposite ends of each individual run of the SMA wire 102 between the plates 104 and 106. For example, the illustrated embodiment may include one pair of wire clamps at opposite ends of each SMA wire 102 defining one of the circular arrangements of SMA wires 102, while the insulating wire guides 108 are used between the opposite ends of the SMA wire 102.

In the embodiment of FIG. 7, the top plate 104 is movable while the bottom plate 106 remains stationary. In particular, the bottom plate 106 is fixed to a base plate 110. As discussed below, a piston in a piston-cylinder assembly is driven by a hydraulic and/or hydrostatic pressure of fluid, thereby driving the plates 104 and 106 to expand away from one another in a manner stretching the SMA wires 102. However, as an electrical current begins flowing through the SMA wires 102, the temperature within the SMA wires 102 increases until it exceeds the transition temperature for the SMA material. Upon exceeding the transition temperature of the SMA wires 102, the SMA wires 102 may begin to contract toward their predetermined shape causing the top and bottom plates 104 and 106 to move toward one another. In this manner, the contracting movement of the plates 104 and 106 drives the piston in the piston-cylinder assembly against the fluid pressure.

FIG. 8 is a cutaway perspective view of the SMA-powered hydraulic accumulator 100 of FIG. 7, illustrating a portion of the SMA wires 102 removed to show internal details. As illustrated, the accumulator 100 includes a piston-cylinder assembly 112 having a piston 111 disposed in a cylinder 113, and a connecting rod assembly 115 coupled to the piston-cylinder assembly 112. The piston-cylinder assembly 113 is coupled to the bottom plate 106, while the connecting rod assembly 115 is coupled to the piston 111 and the top plate 104. In the illustrated embodiment, the connecting rod assembly 115 includes an upper connecting rod 114 and a lower connecting rod 116 coupled together via a turnbuckle 118. Likewise, the lower connecting rod 116 is coupled to the piston 111 via a turnbuckle 120. The illustrated accumulator 100 also includes upper and lower spacer rods 122, spacer plates 124 and 126 (FIG. 9), and a piston-cylinder base 128. The piston-cylinder base 128 secures the piston-cylinder assembly 112 to the bottom plate 106 via bolts 130.

As discussed below, the top plate 104, the connecting rod assembly 115, and the piston 111 move together in response to a fluid pressure change in the cylinder 113 and/or a temperature change of the SMA wires 102 sufficient to contract the SMA wires 102. During this movement, the spacer rods 122 and the spacer plates 124 and 126 are fixed relative to the bottom plate 106 and the cylinder 113 of the piston-cylinder assembly 112, while also guiding and limiting a range of movement of the top plate 104, the connecting rod assembly 115, and the piston 111. For example, the spacer rods 122 support the spacer plates 124 and 126 in stable positions relative to the bottom plate 106 and the cylinder 113, while the spacer plates 124 and 126 enable passage of the connecting rod assembly 115. As the connecting rod assembly 115 passes through the spacer plates 124 and 126, the connecting rod assembly 115 is generally restricted to motion to an axial direction. As discussed below, the spacer rods 122 and the spacer plate 126 limit axial movement of the top plate 104 inwardly toward the bottom plate 106. However, the spacer rods 122 (or extensions) also extend through the top plate 104, and enable movement of the top plate 104. As the spacer rods 122 (or extensions) pass through the top plate 104, the top plate 104 is generally restricted to motion to an axial direction. Operation of the accumulator 100 is discussed in further detail below.

FIG. 9 is a cross-sectional view of the SMA-powered hydraulic accumulator 100 of FIG. 7, illustrating two of the five circular arrangements of SMA wires 102 extending between the plates 104 and 106. As illustrated, the SMA wires 102 extend upwardly through the wire openings 105 in the top plate 104, extend along a curvature of the wire guides 108, and then extend downwardly through the wire openings 105 in the top plate 104 toward the bottom plate 106. At the bottom plate 106, the SMA wires 102 extend downwardly through the wire openings 107 in the bottom plate 106, extend along a curvature of the wire guides 108, and then extend upwardly through the wire openings 107 in the bottom plate 106 toward the top plate 104. In certain embodiments, the accumulator 100 may include a single continuous SMA wire 102 (or bundle of SMA wires) that winds upwardly and downwardly between the top and bottom plates 104 and 106 through all of the wire openings 105 and 107 and associated wire guides 108. However, in the illustrated embodiment, the accumulator 100 may include a continuous SMA wire 102 (or bundle of SMA wires) for each circular arrangement of wire openings 105 and 106 and associated wire guides 108 in the top and bottom plates 104 and 106. At opposite ends of each SMA wire 102 (or bundle of SMA wires), the accumulator 100 includes a wire clamp.

In operation, the top plate 104 moves in response to fluid pressure in the piston-cylinder assembly 112 and/or contraction of the SMA wires 102. Thus, the top plate 104 moves with the connecting rod assembly 115 and the piston 111, while the spacer rods 122 and spacer plates 124 and 126 support and guide the top plate 104, rod assembly 115, and piston 111 to ensure linear motion parallel to the SMA wires 102. For example, the top plate 104 includes rod openings 132 to enable passage of alignment rods 134 coupled to the spacer rods 122. The top plate 104 also includes bushings or bearings 136 mounted in the rod openings 132 around the alignment rods 134. The illustrated bearings 136 are annular shaped bearings with a circular flange or lip 138 mounted along a top surface 140 of the top plate 104. For example, bolts may extend through the lip 138 into the top plate 104 to secure the bearings 136 to the top plate 104.

In the illustrated embodiment, the alignment rods 134 connect to the upper spacer rods 122 via openings 142 in the upper spacer plate 124 and openings 144 in a top portion 148 of spacer rods 122. The alignment rods 134 also include a circular flange or lip 146 to hold the upper spacer plate 124 against the upper spacer rods 122. For example, the alignment rods 134 may thread into the openings 144 to pull the lip 146 downwardly against the upper spacer plate 124 to compressively hold the upper spacer plate 124 between the lip 145 and the top portion 148 of the upper spacer rods 122. As discussed in further detail below, the upper spacer plate 124 surrounds and guides movement of the connecting rod assembly 115, thereby providing support for the axial movement of the top plate 104, the connecting rod assembly 115, and the piston 111. The lip 146 and/or the upper spacer plate 124 also may serve as an axial stop to limit axial movement of the top plate 104 downwardly toward the bottom plate 106 during contraction of the SMA wires 102.

The upper and lower spacer rods 122 are coupled together about the lower spacer plate 126 via studs 152 (e.g., threaded studs). For example, the studs 152 may extend through the lower spacer plate 126 via openings 156, and thread into openings 156 and 158 (e.g., threaded receptacles) in the upper and lower spacer rods 122. As the studs 152 thread into the openings 156 and 158, the upper and lower spacer rods 122 compressively hold the lower spacer plate 126 in position about the connecting rod assembly 115. As discussed in further detail below, the lower spacer plate 126 surrounds and guides movement of the connecting rod assembly 115, thereby providing support for the axial movement of the top plate 104, the connecting rod assembly 115, and the piston 111.

The lower spacer rods 122 are coupled to the cylinder base 128 of piston-cylinder assembly 112 via studs 160. The illustrated studs 160 extend through the cylinder base 128, the bottom plate 106, and spacers 162, while also coupling to the lower spacer rods 122 and the base plate 110. For example, the studs 160 may thread into the lower spacer rods 122, while fixedly coupling (e.g., weld) to the base plate 110. In this manner, the studs 160 securely hold the spacer rods 122, the piston-cylinder assembly 112, the bottom plate 106, and the base plate 110 in a fixed or stationary position relative to one another. As a result, the spacer rods 122 securely hold the spacer plates 124 and 126 about the connecting rod assembly 115, and the spacer rods 122 securely hold the alignment rods 134 in the rod openings 132 through the top plate 104.

The alignment rods 134, the upper and lower spacer rods 122, and the spacer plates 124 and 126 cooperatively support and align the connecting rod assembly 115 and the top plate 104, thereby restricting motion to the linear/axial direction parallel to the SMA wires 102. The lower connecting rod 116 is coupled to a piston rod 164 of the piston 111 via the turnbuckle 120. For example, the turnbuckle 120 may include threads 166 coupled to mating threads on the rods 116 and 164. The lower connecting rod 116 extends through an opening 168, which includes a bushing or bearing 170, in the lower spacer plate 126. The illustrated bearing 170 is an annular shaped bearing with a circular flange or lip 172 mounted along a top surface 174 of the lower spacer plate 126. For example, bolts may extend through the lip 172 into the lower spacer plate 126 to secure the bearing 170 to the lower spacer plate 126. The upper and lower connecting rods 114 and 116 are coupled together (e.g., via threads 175) at the turnbuckle 118. At the upper spacer plate 124, the upper connecting rod 114 extends through an opening 176, which includes a bushing or bearing 178. The illustrated bearing 178 is an annular shaped bearing with a circular flange or lip 180 mounted along a top surface 182 of the upper spacer plate 124. For example, bolts may extend through the lip 180 into the upper spacer plate 124 to secure the bearing 178 to the upper spacer plate 124. The upper connecting rod 114 is coupled to the top plate 104 via a fastener, such as a bolt 184, which threads into openings 186 and 188 in the rod 114 and plate 104. The top plate 104 also includes a bottom surface 190 having a counter bore 192 to receive the upper connecting rod 114, thereby providing alignment and lateral support for the connection between the rod 114, plate 104, and bolt 104.

In operation, the piston 111, the connecting rod assembly 115, and the top plate 104 may move linearly away (direction 196) from the bottom plate 106 in response to fluid pressure in the piston-cylinder assembly 112, while the piston 111, the connecting rod assembly 115, and the top plate 104 may move linearly toward (direction 194) the bottom plate 106 in response to electrical current flowing through the SMA wires 102. As discussed above, the electrical current flowing through the SMA wires 102 gradually increases the temperature of the SMA wires 102 until the temperature exceeds the SMA transition temperature, thereby causing contraction of the SMA wires 102 and thus movement of the top plate 104 toward (direction 194) the bottom plate 106. Upon reducing or removing the electrical current, the SMA wires 120 temperatures will decrease and applied external fluid pressure will expand/stretch SMA, thereby allowing the top plate 104 to move away from the bottom plate 106. During movement in the downward and upward directions 194 and 196, the connecting rod assembly 115 is guided by the bearings 170 and 178 in the spacer plates 124 and 126, and the top plate 104 is guided by the bearings 136 around the alignment rods 134. Furthermore, the wire openings 105 and 107 in the top and bottom plates 104 and 106 maintain alignment and spacing between the SMA wires 102, the wire guides 108 maintain a gradual bend of the SMA wires 102 between adjacent wire openings 105 and 107, and the wire clamps secure the SMA wires 102.

FIG. 10 is a partial perspective view of the SMA-powered hydraulic accumulator 100 of FIG. 7 taken within line 10-10, illustrating details of the insulating wire guides 108. As illustrated, the SMA wires 102 extend along a curved path 200 of the insulating wire guides 108 between adjacent wire openings 105 in the top plate 104. The curved path 200 of the wire guides 108 is configured to reduce stress on the SMA wire 102, while also enabling use of a continuous SMA wire 102 across many wire openings 105 and 107 rather than a severed SMA wire 102 with a wire clamp at each individual wire opening 105 or 107. For example, the curved path 200 may be a semi-circular or U-shaped path, wherein the SMA wire 102 is recessed within the wire guide 108. Thus, the curved path 200 provides lateral support for the SMA wire 102.

The wire openings 105 and 107, in cooperation with the wire guides 108, maintain the spacing and orientation of the SMA wires 102 between the top and bottom plates 104 and 106. As illustrated in FIG. 10, the insulating wire guides 108 are arranged in concentric circular arrangements 202, 204, 206, 208, and 210 on the illustrated top plate 104 as well as the bottom plate 106. In the illustrated embodiment, each circular arrangement 202, 204, 206, 208, and 210 has a continuous SMA wire 102 (or bundle of SMA wires) winding back and forth between the top and bottom plates 104 and 106. As a result, the illustrated embodiment has multiple continuous SMA wires 102 corresponding to the five circular arrangements 202, 204, 206, 208, and 210. In certain embodiments, a single SMA wire 102 (or bundle of SMA wires) may wind back and forth between the top and bottom plates 104 and 106 for all of the wire openings 105 and 107. However, the wire openings 105 and 107 may be arranged with any number of concentric circular arrangements (e.g., 1 to 10) or other patterns.

FIG. 11 is a perspective view of an embodiment of the top plate 104 of the SMA-powered hydraulic accumulator 100 of FIG. 7, illustrating one wire guide 108 exploded from a pair of wire openings 105. The top plate 104 is perforated with a plurality of differently sized openings 105, 132, 188, and 220 extending between the top and bottom surfaces 140 and 190. The wire openings 105 enable passage of the SMA wires 102. The rod openings 132 enable passage of the alignment rods 134. The opening 188 enables passage of the bolt 184 into the upper connecting rod 114. The openings 220 enable passage of fasteners to secure the bearings 136 to the top plate 104. For example, bolts or other threaded fasteners may extend through the lips 138 of the bearings 136 into threaded openings 220.

As illustrated in FIG. 11, the wire guide 108 includes a guide body 222 and a pair of insulating sleeves or spacers 224. The guide body 222 includes the curved path 200, which may be recessed into the body 222. The insulating spacers 224 are disposed on opposite ends of the curved path 200 in alignment with adjacent wire openings 105 in the top plate 104. In the illustrated embodiment, the insulating spacers 224 are hollow cylindrical structures made of an insulating material (e.g., thermal and/or electrically insulating material), wherein an outer diameter of the spacers 224 is sized to fit within the wire openings 105 and an inner diameter of the spacers 224 is sized to pass the SMA wire 102. Accordingly, the insulating spacers 224 may be inserted securely into the wire openings 105 to electrically and/or thermally isolate the SMA wires 102 from the top plate 104. Similarly, the insulating spacers 224 may be inserted securely into the wire openings 107 to electrically and/or thermally isolate the SMA wires 102 from the bottom plate 106. In certain embodiments, the insulating spacers 224 may be secured to the wire openings 105 and 107 via a threaded interface, an adhesive, an interference or press fit, or another suitable connection.

Although the illustrated guide body 222 is an independent structure, some embodiments may integrate a plurality of guide bodies 222 with the top plate 104, the bottom plate 106, and/or the spacers 224. For example, the plates 104 and 106 may be cast and/or machined to include a plurality of wire openings 105 and 107 and associated guide bodies 222. The guide bodies 222 may be recessed into the plates 104 and 106, or the guide bodies 222 may protrude from the plates 104 and 106. However, any suitable construction is within the scope of the disclosed accumulator 100.

Similarly, although the illustrated spacers 224 are independent structures, some embodiments may integrate the insulating spacers 224 with the SMA wires 102, the top plate 104, the bottom plate 106, or the guide body 222. For example, an insulating coating may be applied to the SMA wires 102, the top plate 104, and/or the bottom plate 106. The insulating coating may be limited to the wire openings 105 and 107, or may extend onto other areas of the SMA wires 102, the top plate 104, the bottom plate 106, or the guide body 222. In one embodiment, each SMA wire 102 may include an insulating sleeve or coating along an entire length of the SMA wire 102. In another embodiment, the top and bottom plates 104 and 106 may be entirely coated with an insulating material. By further example, the wire guide 108 may be a one-piece structure including the guide body 222 and the spacers 224, wherein the one-piece structure is entirely made of or coated with an electrically insulating material.

In the illustrated embodiment, the top and bottom plates 104 and 106 are circular in shape. In some embodiments, the top and bottom plates 104 and 106 may have non-circular shapes, such as oval, rectangular, triangular, hexagonal, or other suitable shapes. The top and bottom plates 104 and 106 also may have a variety of patterns or distributions of wire openings 105 and 107, which may be based at least partially on the shape of the plates 104 and 106. For example, the illustrated circular plates 104 and 106 have the concentric circular arrangements 202, 204, 206, 208, and 210 of wire openings 105 and 107. In contrast, rectangular shaped plates 104 and 106 may have linear rows and columns of wire openings 105 and 107.

FIG. 12 is an exemplary embodiment of the wire guide 108. As illustrated, the wire guide 108 includes the guide body 222 and the pair of insulating spacers 224. The guide body 222 has a flat bottom surface 240 and a curved top surface 242, which includes the curved path 200 recessed to define a curved groove 244 (e.g., U-shaped groove). The curved groove 244 has a width W sized to fit the SMA wire 102. The curved surface 242 defines a radius of curvature R, which may be selected based on the spacing between adjacent wire openings 105 or 107, the diameter of the SMA wire 102, and other considerations. The radius of curvature R may be configured to reduce stress in the SMA wires 102, while also enabling use of a continuous length of SMA wire 102 across multiple wire openings 105 and 107.

As illustrated, the insulating spacers 224 have a cylindrical outer surface 246, a ring-shaped top surface 248, a ring-shaped bottom surface 250, and a wire passage 252 extending between surfaces 248 and 250. The wire passage 252 may be sized equal to or greater than the diameter of the SMA wire 102. The insulating spacers 224 generally align the wire passages 252 with opposite ends of the curved groove 244 of the guide body 222, thereby defining a U-shaped path through the plates 104 and 106 from one side to another. The illustrated spacers 224 may have a smooth cylindrical outer surface 246 configured to fit loosely or press-fit securely into the wire openings 105 and 107. However, the cylindrical outer surface 246 of the spacers 224 may include surface roughness, threads, or a taper to provide more secure mounting in the wire openings 105 and 107. In certain embodiments, the spacers 224 may extend partially or completely (e.g., 25 to 100 percent) through the wire openings 105 and 107. However, the spacers 224 may remain in close proximity, or in contact with, the guide bodies 222 of the wire guides 108.

The wire guide 108 may be made at least partially or substantially of metal, ceramic, plastic, or some combination thereof. For example, the guide body 222 and spacers 224 may be made of steel with an insulating coating. By further example, the guide body 222 and spacers 224 may be made entirely of an insulating material, such as a plastic or ceramic. The insulating material may be selected to provide electrical insulation and thermal insulation sufficient for the SMA materials used for the SMA wires 102.

FIG. 13 is a partial perspective view of an embodiment of the SMA-powered hydraulic accumulator 100 of FIG. 7 taken within line 13-13, illustrating details of wire clamps 260. As illustrated, the wire clamps 260 are coupled to opposite end portions 262 and 264 of the SMA wire 102 (e.g., continuous SMA wire) in the circular arrangement 210. In other words, the illustrated SMA wire 102 represents a single continuous SMA wire 102 that winds back and forth between the top and bottom plates 104 and 106 until a full circle (or any other suitably configured shape-arrangement) is completed as indicated by the opposite end portions 262 and 264. In the illustrated embodiment, a pair of wire clamps 260 is used to secure the opposite end portions 262 and 264 of each SMA wire 102 used in one of the concentric circular arrangements 202, 204, 206, 208, and 210. In other embodiments, a greater or lesser number of clamps 260 may be used depending on the pattern of wire openings 105 and 107, and the number of SMA wires 102 used to wind back and forth between these openings 105 and 107.

FIG. 14 is a perspective view of an embodiment of the bottom plate 106 of the SMA-powered hydraulic accumulator 100 of FIG. 7, illustrating a wire guide 108 and a wire clamp 260 exploded from wire openings 107 in the bottom plate 106. The bottom plate 106 is perforated with a plurality of differently sized openings 107, 274 and 276 extending between top and bottom surfaces 270 and 272. The wire openings 107 enable passage of the SMA wires 102. The openings 274 enable passage of the studs 160. The opening 276 enables passage of the bolts to secure the piston-cylinder assembly 112 to the bottom plate 106. The openings 220 enable passage of fasteners to secure the bearings 136 to the bottom plate 106. For example, bolts or other threaded fasteners may extend through the lips 138 of the bearings 136 into threaded openings 220. As further illustrated, the wire guide 108 is aligned with a pair of wire openings 107 in the bottom plate 106, similar to the alignment with wire openings 105 in the top plate 104 as shown in FIG. 11. Likewise, the wire clamp 260 is aligned with a wire opening 107 in the bottom plate 106, similar to the alignment with the wire opening 105 in the top plate 104 as shown in FIG. 13.

FIGS. 15, 16, and 17 illustrate an embodiment of the wire clamp 260 of FIGS. 13 and 14. FIG. 15 is a perspective view of an embodiment of the wire clamp 260, illustrating opposite wire clamp plates 280, bolts or fasteners 282 extending through the wire clamp plates 280, and an insulating spacer or sleeve 284. The insulating spacer 284 is configured to space the wire clamp plates 280 and bolts 282 at an offset away from the top and bottom plates 104 and 106, thereby electrically and thermally isolating the wire clamp plates 280 and the bolts 282 from the plates 104 and 106. The spacer 284 has a cylindrical outer surface 286, a wire passage 288, a ring-shaped top surface 290, and a ring-shaped bottom surface 292. As discussed below, the wire passage 288 routes the SMA wire 102 in between the opposite wire clamp plates 280, which are compressed together about the SMA wire 102 via the bolts 282.

FIG. 16 is a perspective view of an embodiment of one of the wire clamp plates 280 of FIG. 15. The clamp plate 280 has a front face 294, a rear face 296, and a pair of openings 298 extending between the faces 294 and 296. The openings 298 are configured to receive the bolts 282. The clamp plate 280 also has a top surface 300, a bottom surface 302, and a groove 304 extending along the face 294 from the top surface 300 to the bottom surface 302. The groove 304 is aligned with the wire passage 288 of the spacer 284, such that it can receive the SMA wire 102. In certain embodiments, the groove 304 may be sized smaller than (e.g., 50 to 90 percent of) the radius of the SMA wire 102.

FIG. 17 is a top view of an embodiment of the wire clamp 260 of FIG. 15. As illustrated, the wire passage 288 of the spacer 284 is aligned with the grooves 304 in the opposite wire clamp plates 280, and the bolts 282 extend through the openings 298 in the opposite wire clamp plates 280. In the illustrated embodiment, the bolts 282 include threads 306 to mate with threads in at least the distal wire clamp plate 280, thereby enabling the bolt 282 to compress the plates 280 toward one another about the SMA wire 102. In operation, the bolts 282 may be loosened to separate the wire clamp plates 280, and thus widen the gap between the grooves 304. The SMA wire 102 may then be inserted through the wire passage 288 of the spacer 284 into the space between the grooves 304. Finally, the bolts 282 may be tightened to compress the wire clamp plates 280 about the SMA wire 102.

The wire clamp 260 may be made at least partially or substantially of metal, ceramic, plastic, or some combination thereof. For example, the clamp plates 280, the bolts 282, and the spacer 284 may be made of steel with an insulating coating. By further example, the clamp plates 280, the bolts 282, and the spacer 284 may be made entirely of an insulating material, such as a plastic or ceramic. However, in the illustrated embodiment, the spacer 284 may be made of an insulating material, whereas the clamp plates 280 and the bolts 282 may be made of a metal or non-insulating material. In certain embodiments, the SMA wire 102 may be coated or wrapped with an insulating material. The insulating material may be selected to provide electrical insulation and thermal insulation sufficient for the SMA materials used for the SMA wires 102.

Having provided a detailed description of various embodiments and features of the SMA-powered hydraulic accumulator 100 disclosed herein, embodiments of an ultracapacitor-based power supply which may be utilized for actuating SMA elements (e.g., SMA wires, cables, films, etc.) of the hydraulic accumulator 100 are now discussed and illustrated in further detail. Further, while discussed in the context of an SMA-powered hydraulic accumulator (e.g., 100), it should be appreciated that the ultracapacitor-based power supply may be configured to drive any suitable SMA-actuated component, and should not be viewed as being limited to subsea hydraulic accumulators.

As discussed above, ultracapacitors (also referred to as electric double-layer capacitors) may offer several benefits over other solutions for driving SMA-powered equipment. For instance, while a current for actuating SMA elements may be provided by a surface AC or DC power supply, such power supplies typically have a large form factor and are difficult and inconvenient to transport. Depending on the application, SMA actuators may be actuated using DC power or AC power. For instance, for larger SMA actuator applications, AC grid power may also be utilized to supply energy for driving an SMA element. For smaller SMA actuators applications, the voltage supplied by an AC power grid may be reduced to a suitable range to avoid melting and/or damaging the SMA wires. However, it should be understood that in certain settings, such as subsea applications, grid power is not always readily available. Additionally, other types of devices may be used to actuate SMA elements, as discussed below.

In some instances, batteries (e.g., lead-acid batteries) may be used to overcome some of the disadvantages of using conventional power supplies or grid power for the actuation of SMA elements. However, the use of batteries is not without its own drawbacks. For instance, while batteries may be configured to supply the current for actuating SMA elements, the charging and discharging cycles of batteries are generally difficult to manage or regulate. Particularly, batteries generally are unable to completely discharge, and may also rely on a specific type of charging cycle (for recharging) depending on the type of battery technology being utilized (e.g., lead-acid, nickel-cadmium, nickel-metal hydride, lithium-ion, etc.). Furthermore, some batteries may exhibit limited cycle life, meaning that as the battery is repeatedly charged/recharged and discharged over time, the overall capacity of the battery cells gradually decreases.

As discussed above, ultracapacitors may offer several advantages over applications that utilize AC/DC power supplies, grid power, batteries, and conventional capacitors. As will be appreciated, conventional capacitors generally include a dielectric material, which provides an insulating barrier, disposed between two conductive plates or electrodes. When an electric field is present in the dielectric, charge carriers (e.g., electrons) migrate from one conductive plate to the other and generate a potential difference across the conductive plates, thus providing stored energy which may be discharged and used to drive a circuit or load.

With ultracapacitors, rather than utilizing a conventional dielectric (e.g., an insulating barrier), two “conductive plates” may each be formed by an electrode and a substrate. Both plates may be formed using the same substrate having the same electrical properties, hence the term “electric double-layer.” In certain embodiments, the substrate may include a nanoporous material, which may be carbon-based (e.g., activated charcoal, carbon nanotubes, carbon aerogels, etc.). A dielectric medium, which may be very thin and narrow relative to the dielectric material of conventional capacitors, may be suspended within the nanoporous material, to provide a separating medium for the two plates. As will be appreciated, due to the nature of nanoporous materials (e.g., having low-density volume of particles with intervening holes), the overall surface area of each conductive plate may be considerably greater than that of conductive plates used in conventional capacitors. Thus, in conjunction with the narrow dielectric medium, the conductive plates of ultracapacitors may exhibit a charge potential (e.g., capacitance) that may, in some instances, be exponentially greater than the capacitance provided by conventional capacitors of a similarly sized package. By way of example, while a conventional capacitor generally stores energy on the order of micro-farads or nano-farads, similarly sized ultracapacitors may be configured to store energy on the order of farads (e.g., between approximately 1 to 5000 F or more or, more specifically, between approximately 10 to 1000 F or, even more specifically between approximately 150 to 300 F).

As discussed above, certain embodiments of the present disclosure provide for a power supply that utilizes one or more ultracapacitors to provide energy (e.g., current) to actuate an SMA element, such as an SMA cable, wire, or film of the above-described SMA-powered hydraulic accumulator 100. Particularly, due to their high energy potential relative to conventional capacitors, ultracapacitors may function as a temporary battery in such a power supply, which may be continuously charged by a DC source, discharged to provide current to drive the SMA elements, and then recharged. Further, when compared to conventional DC or AC power supply units, ultracapacitors are generally more portable and easier to transport. Ultracapacitors may also have the flexibility to be recharged by multiple types of sources, and have the ability to reach a full charge in a relatively short amount of time, often on the order of seconds (e.g., between approximately 1-200 seconds). As will be appreciated, charge time may be directly dependent upon capacitance size, voltage, internal resistance, and so forth. By way of example only, a 48V 110 F capacitor may be completely discharged at a rate 200 A in approximately 30 seconds, and may also be charged at the same rate in the approximately the same amount of time. Additionally, ultracapacitors may provide a high power output and exhibit a long operational life compared to batteries, as they generally do not exhibit the cycle life limitations of certain batteries, and may be fully charged and discharged repeatedly (e.g., hundreds of thousands or even millions of charge cycles) with little if any degradation in their ability to retain a full charge. Further, ultracapacitors are also RoHS compliant, whereas not all batteries are. For at least these reasons, among others, ultracapacitors may offer an ideal solution for actuating SMA elements in various applications, such as subsea mineral extraction applications.

With these points in mind, FIG. 18 provides a simplified block diagram view showing an embodiment of an SMA-powered application 307. The application 307 includes multiple SMA load elements 322 a-322 d. As discussed above, the SMA elements may be configured as SMA wires, cables, films, and so forth. As discussed above, SMA-powered equipment, such as the hydraulic accumulator 100, may utilize any suitable number of SMA elements. For instance, in FIG. 18, the SMA elements 322 a-322 d represent “N” total elements, with SMA load 322 a presenting a first SMA element, SMA load 322 b representing a second SMA element, and so forth. By way of example, with regard to the embodiment of the hydraulic accumulator shown in FIG. 7, each concentric circular arrangement on the top and bottom plates 104 and 106 may represent one SMA wire, and thus one SMA load. Additionally, in some embodiments, SMA loads may be formed as a series of plates 104, 106 to form a single SMA load with higher resistance load. For instance, in an embodiment employing concentric circular arrangements, one SMA load (e.g., 322 a) may be formed by all pairs of 104 and 106 in the outer-most circle.

With regard to the illustrated application 307, each of the SMA loads 322 a and 322 b may be actuated by separate respective ultracapacitor-based power supplies 310 a and 310 b. Generically, these power supplies may be referred to by reference number 310. As shown, each of the power supplies 310 a and 310 b may receive separate respective DC signals 312 a and 312 b for charging one or more ultracapacitors associated each power supply. As will be discussed further below, the power supply 310 may include control circuitry (e.g., controllers, regulators, etc.) for charging and for discharging the ultracapacitor to provide a current for actuating a respective SMA load. Additionally, it should be appreciated that the DC signals 312 a and 312 b may be provided from separate DC sources or from the same DC source.

The power supply 310 c of FIG. 18 may be configured receive a DC signal 312 c and to charge an ultracapacitor in a manner similar to the power supplies 310 a and 310 b, except that the power supply 310 c may be configured, as shown in FIG. 18, to actuate multiple SMA loads, such as the SMA loads 322 c and 322 d. For instance, in the illustrated embodiment, a switching element 305 may be provided at the output of the power supply 310 c, and may be configured to provide an actuating current to either the SMA load 322 c or 322 d depending, for instance, upon a control signal.

The application 307 of FIG. 18 also includes a control unit 308. As will be appreciated, while each power supply 310 may include their own respective controllers and/or regulators (e.g., for controlling the charging and discharging cycles of ultracapacitors), the control unit 308 may provide additional control signals 309 to each of the power supplies 310. In one embodiment, these additional control signals 309 may function to generally synchronize the actuation of the SMA loads 322 being driven by the power supplies 310. For instance, additional circuitry within the power supplies 310 (e.g., charge and discharge controllers and/or regulators) may respond to the control signals 309 to control the charging and discharging of their respective ultracapacitors, such that their respective SMA loads 322 are actuated in a generally synchronous manner. For instance, under control of the controller 307, the SMA loads may be controlled in a generally synchronous manner such that during actuation, they transition between the Martensite and Austenite states at approximately the same time and/or rate. This may be particularly useful in applications, such as the hydraulic accumulator 100 (FIG. 7), where multiple SMA elements are used simultaneously to power a device. In one embodiment, the control unit 308 may include a user interface, such as a graphical user interface, which may allow an operator to control or set various parameters for actuating the SMA elements 322. Further, it should be noted that in a subsea application where the SMA elements 322 are located under water, the control unit 308 may be located remotely with respect to the SMA elements (e.g., on the surface of a rig 16).

Referring to FIG. 19, a circuit schematic is illustrated and shows an embodiment of an ultracapacitor-based power supply 310 that may be configured to actuate a load 322, which may represent an SMA element, such as an SMA wire, cable, or film. The operation of the power supply 310 will be further described below with respect to FIGS. 20 and 21. As shown in FIG. 19, the power supply 310 may include a DC supply source 312, a DC charge controller or regulator 314, a charging switch 316, an ultracapacitor 318, a discharge switch 320, the load 322, and a discharge controller 324. Examples of DC sources 312 that may be implemented in various embodiments include wind power sources (e.g., located on a surface rig), sources for harvesting energy from ocean currents, sources for harvesting energy from pipe vibrations, subsea DC supply lines, or any other suitable source or combination thereof. Indeed, it should be understood that ultracapacitors provide the flexibility to be charged using a wide variety of regulated and unregulated power sources.

FIG. 19 may represent an initial state in which both the charging switch 316 and the discharge switch 320 are in the open state and in which the ultracapacitor 318 is presently in a discharged state. In operation, control signal 326 from the DC charge controller 314 and control signal 328 from the discharge controller 324 may provide the signals to control the states of the switching elements 316 and 320, respectively.

As shown in FIG. 20, during operation, the charging switch 316, upon receiving an appropriate control signal 326, may transition to a closed state, thus providing a path for a DC signal provided by the DC supply source 312 to charge the ultracapacitor 318. In one embodiment, the DC supply source may supply a DC voltage of approximately 24 VDC. The DC charge controller 314, which may be a regulator, controller, or DC-to-DC switching converter, may be configured to maintain the voltage, current, and/or power delivered to the ultracapacitor 318 at a generally constant level. Additionally, the DC charge controller 314 may be configured to accept a range of input DC voltages while maintaining a target DC output level to the ultracapacitor 318. By way of example, in one embodiment, the power supply 310 may accept a DC input having range of between approximately 3 to 24 volts (VDC), and the DC charge controller 314 may maintain its DC output at a particular DC level. In one embodiment, the output of the DC charge controller 314 may be maintained at approximately 46 VDC. In other embodiments, the output of the DC charge controller 314 may be in a range of between approximately 24 VDC to 300 VDC. By way of example only, in certain embodiments, the DC charge controller 314 may be a model LT1083, LT1084, or LT1085 regulator, or a model LT3750 or LT3751 charge controller, available from Linear Technology Corporation of Milpitas, Calif.

As shown in FIG. 20, once the charging switch 316 is closed, the current, i_(c), charges the ultracapacitor 318. As discussed above, the ultracapacitor may be charged relatively quickly, i.e., (e.g., between 1-200 seconds). In one embodiment, the ultracapacitor 318 may have a capacitance of between approximately 50 to 500 farads (F). A sensing or feedback line 330 is provided, as shown in FIG. 20, to measure the voltage across the ultracapacitor 318 to determine when the capacitor is fully charged. For instance, the DC charge controller 314 may be configured or programmed to store the known voltage of the ultracapacitor 318 when in a full-charged state, or may be configured to sense when the ultracapacitor 318 has reaches its full charge potential, which may be determined using the following expression:

$\begin{matrix} {{E = {\frac{1}{2}{CV}_{UC}^{2}}},} & \left( {{Equation}\mspace{14mu} 1} \right) \end{matrix}$ wherein E represents the full stored energy potential in joules, C represents the capacitance value of the ultracapacitor 318, and V_(UC) represents the voltage across the ultracapacitor 318.

To provide one example, the ultracapacitor 318, in one embodiment, may have a capacitance of approximately 250 farads and a voltage rating of approximately 48 volts. Assuming these conditions, the DC charge controller 314 may be configured to stop charging the ultracapacitor 318 (e.g., by opening the switch 316) when either the voltage V_(UC) measured via the feedback line 330 reads 48 VDC, or when the DC charge controller 314 determines, based upon the voltage provided via feedback line 330, that the ultracapacitor 318 has been charged to its full potential. For instance, in the present example, the fully charged ultracapacitor 318 may store approximately 288 Kilo-Joules (288,000 Joules) of energy. Further, while the power supply 310 is depicted herein as having a single ultracapacitor 318, some embodiments of the power supply 310 may include multiple ultracapacitors. For instance, multiple ultracapacitors (e.g., 2, 3, 4, 5, or more) may be arranged in a parallel configuration to provide the total desired capacitance.

Continuing to FIG. 21, once the ultracapacitor 318 is determined to be fully charged, the switch 316 is opened by the DC charge controller 314 (via sending control signal 326), and the charge stored in the ultracapacitor 318 may be discharged to provide a current, i_(d), for actuating the SMA load 322. During the discharge cycle, the discharge controller 324 may control the rate at which the ultracapacitor 318 is discharged. For instance, ultracapacitors 318, due to their high energy density and storage potential, may (without regulation) discharge current at rates of as much as 200 ampere-hours (Ah) or more. As will be appreciated, without regulating this output, such high current levels may damage the SMA element being actuated. In one embodiment, output current i_(d) may be regulated by periodically toggling the state of the discharge switch 320 between open and closed positions. For instance, the discharge controller 324 may include a pulse-width-modulation (PWM) signal generator/controller that provides a control signal 328 to the switch 320 in the form of a PWM signal. For example, in one embodiment, the control signal 328 may be a PWM signal having a frequency of between approximately 1 to 500 hertz or, more specifically, between approximately 1 to 250 hertz, or even more specifically, between approximately 1 to 100 hertz. By modulating the frequency of the PWM signal, the current delivered to the SMA load 322 may be controlled. In this manner, the ultracapacitor 318 may be discharged at a controlled rate to actuate the SMA load 322.

In one embodiment, the resistance of each SMA load 322 may be between approximately 0.1 to 1 ohms. Further, it should be appreciated that additional sensors (e.g., sensors 80 of FIG. 5 or sensors 92 of FIG. 6) may also be provided and may sense one or more conditions indicating when the SMA load 322 is fully actuated (e.g., fully transitioned to the Austenite state). This sensor data may be provided to the discharge controller 324, which may adjust the discharge rate to, for example, maintain the SMA load 322 in its actuated state or, if the application 307 indicates that the SMA load 322 is to be de-actuated (e.g., returns from the heated Austenite state to the cooler Martensite state), the discharge controller 324 may control the switch 320 to an open state, where it may remain until the SMA load 322 is to be actuated again. As will be appreciated, at this point, the ultracapacitor 318, which is presently not being discharged, may be recharged by the DC supply 312.

With regard to the switching elements 316 and 320, these may be implemented in certain embodiments using solid state switches (e.g., solid state relays and/or transistors), including for example, bipolar junction transistors (BJT), MOSFETS, and so forth. For instance, referring to FIG. 22, a more detailed circuit schematic showing an embodiment of the power supply 310 is illustrated in which each of the switching elements 316 and 320 are provided as single BJTs. In other embodiments, the switching elements 316 and 320 may be provided as MOSFETs, or a combination of MOSFETs or BJTs.

As further illustrated in FIG. 22, the power supply may also include the diode 336 and the inductor 338. The inductor 338 may be configured to control the flow of the current through the SMA load 322. For instance, in a situation where a large or sudden current is discharged from the ultracapacitor 318, the inductor may regulate the output to prevent excessive current flow to the SMA load 322, which may prevent sparking and/or damage to the SMA load 322. The diode 336 may be configured to block negative voltage from the inductor (e.g., to prevent backflow of current). By way of example only, the diode 336 may be implemented as a flyback diode.

FIG. 23 illustrates another embodiment of the power supply 310, wherein the switching element 316 is implemented as a pair of MOSFET transistors 342 and 344, and wherein the switching element 320 is also implemented as a pair of MOSFET transistors 348 and 350. As will be appreciated, the back-to-back configuration of MOSFET transistors 342, 344 and 348, 350 may increase current flow while lowering heat dissipation.

Next, FIG. 24 illustrates a flow chart depicting an embodiment of a method 360 for actuating an SMA element using an ultracapacitor-based power supply (e.g., 310). Beginning at step 362, a charging switch (e.g., switch 316) is closed to initiate charging of an ultracapacitor (e.g., 318), such as by using a DC source (e.g., 312). At step 364, the ultracapacitor voltage is monitored to determine whether a full charge has been obtained. For instance, as discussed above in FIGS. 19-21, the feedback signal 330 may provide a voltage reading (V_(UC)) to the DC charging circuitry 314. Decision logic 366 determines whether the ultracapacitor 318 is fully charged. If the ultracapacitor 318 is not yet fully charged, the method 360 returns to step 364, and the ultracapacitor 318 continues to charge. If the ultracapacitor 318 is determined to be fully charged, then the method 360 continues to step 368, and the charging switch 316 is opened. Next, at step 370, the ultracapacitor is discharged at a controlled rate, such as by using a PWM signal, to deliver an actuation current to actuate an SMA element. In some embodiments, a decision block prior to step 370 ay determine if the SMA element needs to be actuated and, if so, the method 360 may continue to step 370. If the SMA element does not need to be actuated, the method may return to step 364 and implement a trickle charge mode to maintain the charge of the ultracapacitor 318 (e.g., due to possible internal energy losses).

FIG. 25 shows a graph 380 depicting five discharge profiles of an ultracapacitor 318. For instance, the graph 380 may represent the discharge profiles of an ultracapacitor having a voltage of approximately 48 V when fully charged and a capacitance of 110 farads discharged at different current rates. For instance, as shown by the curve 382, at a discharge current of 10 amps (Ah), the ultracapacitor 318 will still retain approximately half of its full-capacity voltage, and thus approximately 25% of its full energy potential, after 240 seconds. Similarly, the curves 384, 386, 388, 390, and 392 illustrate the discharge profile of the ultracapacitor at rates of 20, 50, 100, 150, and 200 Ah. As discussed above, the current delivered to the SMA load may be controlled by modulating the frequency at which the discharge switch opens and closes (e.g., by modulating the frequency of a PWM control signal).

As will be understood, the various techniques described above and relating to actuation of SMA elements (e.g., SMA wires, cables, films, etc.) using an ultracapacitor-based power supply are provided herein by way of example only. Accordingly, it should be understood that the present disclosure should not be construed as being limited to only the examples and embodiments provided above. Indeed, a number of variations for charging and discharging an ultracapacitor to actuate an SMA load may exist. Further, it should be appreciated that the above-discussed techniques for controlling the charging and discharging of the ultracapacitor (e.g., as carried out by the DC charge controller 314 and the discharge controller 324) may be implemented in any suitable manner. For instance, these processes may be implemented using hardware (e.g., suitably configured circuitry), software (e.g., via a computer program including executable code stored on one or more tangible computer readable medium), or via using a combination of both hardware and software elements.

While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims. 

The invention claimed is:
 1. A system, comprising: a cylinder; a piston disposed within the cylinder and configured to move along an axis of the cylinder; a plurality of shape memory alloy (SMA) elements, each extending lengthwise along the axis of the cylinder and configured to actuate the piston within the cylinder; and a power supply comprising: a capacitor configured to be charged by a DC source and to discharge an electrical current at a first rate; a first switch configured to enable charging of the capacitor by the DC source when in a first closed position, and to disable charging of the capacitor when in a first open position; and a second switch configured to enable discharging of the capacitor when in a second closed position, and to disable discharging of the capacitor when in a second open position; wherein the power supply is configured to regulate discharge of the capacitor to reduce a rate of the discharge of the electrical current from the first rate to a second rate to actuate the plurality of SMA elements lengthwise along the axis, wherein the second rate of the electrical current is below a threshold rate to protect the plurality of SMA elements and causes a phase transformation of the plurality of SMA elements from a first phase to a second phase.
 2. The system of claim 1, wherein the power supply comprises a DC charge controller configured to regulate a DC voltage provided by the DC source for charging the capacitor.
 3. The system of claim 2, wherein the DC charge controller is configured to provide a first control signal to the first switch, and the first switch is configured to transition to the first closed position or the first open position depending on a state of the first control signal.
 4. The system of claim 3, wherein the DC charge controller is configured to determine when the capacitor is charged to a fully-charged state and, if the capacitor is in the fully-charged state, to cause the first switch to transition to the first open position to disable charging of the capacitor.
 5. The system of claim 1, wherein the power supply comprises a discharge controller configured to regulate the discharge of the capacitor by providing a second control signal, and the second control signal causes the second switch to repeatedly transition between the second closed position and the second open position at a frequency to provide the electrical current for actuating the plurality of SMA elements lengthwise along the axis.
 6. The system of claim 5, wherein the second control signal comprises a pulse-width modulation signal, and the discharge controller comprises circuitry configured to generate the pulse-width modulation signal.
 7. The system of claim 6, wherein the pulse-width modulation signal has a frequency of between approximately 1 to 100 hertz.
 8. The system of claim 6, wherein the electrical current for actuating the plurality of SMA elements is adjustable by modulating the frequency of the pulse-width modulation signal.
 9. The system of claim 1, wherein the capacitor has a capacitance of between approximately 200 to 300 farads.
 10. The system of claim 1, wherein the plurality of SMA elements comprises at least one of an SMA wire, SMA cable, SMA film, or a combination thereof.
 11. The system of claim 1, wherein the plurality of SMA elements comprises a plurality of SMA wires extending along one another, or at least one SMA wire that winds back and forth.
 12. The system of claim 1, wherein the capacitor comprises at least one ultracapacitor.
 13. The system of claim 1, wherein the power supply is configured to control the rate of the discharge of the electrical current to maintain the plurality of SMA elements in the second phase.
 14. The system of claim 1, wherein the threshold rate of the electrical current causes the plurality of SMA elements to heat to a melting temperature of the plurality of SMA elements.
 15. The system of claim 14, wherein the second rate causes the plurality of SMA elements to heat to a first temperature less than the melting temperature, but greater than a transition temperture of the phase transformation.
 16. The system of claim 1, wherein the piston is configured to drive a subsea mineral extraction component.
 17. The system of claim 1, wherein the piston is configured to drive an accumulator. 